Vehicles sold in North America are required to adsorb refueling, diurnal and running loss vapors into a carbon canister. When the canister is loaded with fuel vapor, the contents may be purged to engine intake using engine intake vacuum to draw fresh air though the canister, desorbing bound hydrocarbons. Strict regulations regulate the performance of evaporative emissions systems.
As such, evaporative emissions systems must be periodically subject to on-board testing for leaks and other forms of degradation that could increase emissions. In hybrid vehicles, and other vehicles configured to operate in engine-off or reduced manifold vacuum modes opportunities to test for leaks using manifold vacuum may be infrequent. As such, an additional vacuum source is required for leak testing evaporative emissions systems in these vehicles. In some examples, a vacuum pump is placed between the fuel vapor canister and atmosphere.
However, such vehicles also have infrequent opportunities to purge the fuel vapor canister to the intake of the engine. Subsequently, if a leak test is applied to the fuel vapor canister while it is saturated with fuel vapor, hydrocarbon breakthrough may occur and result in bleed emissions as well as false leak detection. Hydrocarbon breakthrough may be detected by a dedicated hydrocarbon sensor, as shown in U.S. Patent Application 2013/0152905, but this adds significant manufacturing costs to the vehicle.
In one example, the issues described above may be addressed by a method for a fuel system, comprising applying a vacuum to a fuel vapor canister side of the fuel system, and indicating hydrocarbon breakthrough responsive to a fuel vapor canister side pressure inflection point indicative of a decay in fuel vapor canister side vacuum. In this way, an evaporative leak check module may perform a leak check on a fuel vapor canister, while hydrocarbon breakthrough from the fuel vapor canister may be indicated without requiring a dedicated hydrocarbon sensor in the canister vent line.
As one example, a pressure inflection point may lead to the cessation of applying vacuum to the fuel vapor canister side of the fuel system, thus preventing hydrocarbon breakthrough. Further, the leak test may be revisited once the fuel vapor canister has been purged. In this way, the leak test may occur without risk of false failures due to hydrocarbon breakthrough.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.